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<refentry id="yasm">

 <refentryinfo>
  <title>The Yasm Modular Assembler</title>
  <date>April 2007</date>
  <productname>Yasm</productname>
  <author>
   <firstname>Peter</firstname>
   <surname>Johnson</surname>
   <affiliation>
    <address><email>peter@tortall.net</email></address>
   </affiliation>
  </author>

  <copyright>
   <year>2004</year>
   <year>2005</year>
   <year>2006</year>
   <year>2007</year>
   <holder>Peter Johnson</holder>
  </copyright>
 </refentryinfo>

 <refmeta>
  <refentrytitle>yasm</refentrytitle>
  <manvolnum>1</manvolnum>
 </refmeta>

 <refnamediv>
  <refname>yasm</refname>
  <refpurpose>The Yasm Modular Assembler</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>yasm</command>
   <arg choice="opt">
    <option>-f <replaceable>format</replaceable></option>
   </arg>
   <arg choice="opt">
    <option>-o <replaceable>outfile</replaceable></option>
   </arg>
   <arg choice="opt" rep="repeat">
    <option><replaceable>other options</replaceable></option>
   </arg>
   <arg choice="req"><replaceable>infile</replaceable></arg>
  </cmdsynopsis>

  <cmdsynopsis>
   <command>yasm</command>
   <arg choice="plain">
    <option>-h</option>
   </arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>The Yasm Modular Assembler is a portable, retargetable
   assembler written under the <quote>new</quote> (2 or 3 clause) BSD
   license.  Yasm currently supports the x86 and AMD64 instruction
   sets, accepts NASM and GAS assembler syntaxes, outputs binary,
   ELF32, ELF64, COFF, Win32, and Win64 object formats, and generates
   source debugging information in STABS, DWARF 2, and CodeView 8
   formats.</para>

  <para>YASM consists of the <command>yasm</command> command, libyasm,
   the core backend library, and a large number of modules.
   Currently, libyasm and the loadable modules are statically built
   into the <command>yasm</command> executable.</para>
    
  <para>The <command>yasm</command> command assembles the file infile
   and directs output to the file <replaceable>outfile</replaceable>
   if specified. If <replaceable>outfile</replaceable> is not
   specified, <command>yasm</command> will derive a default output
   file name from the name of its input file, usually by appending
   <filename>.o</filename> or <filename>.obj</filename>, or by
   removing all extensions for a raw binary file.  Failing that, the
   output file name will be <filename>yasm.out</filename>.</para>

  <para>If called with an <replaceable>infile</replaceable> of
   <quote>-</quote>, <command>yasm</command> assembles the standard
   input and directs output to the file
   <replaceable>outfile</replaceable>, or
   <filename>yasm.out</filename> if no
   <replaceable>outfile</replaceable> is specified.</para>
 </refsect1>

 <refsect1>
  <title>Options</title>

  <para>Many options may be given in one of two forms: either a dash
   followed by a single letter, or two dashes followed by a long
   option name.  Options are listed in alphabetical order.</para>

  <refsect2>
   <title>General Options</title>

   <variablelist>
    <varlistentry>
     <term><option>-a <replaceable>arch</replaceable></option> or
      <option>--arch=<replaceable>arch</replaceable></option>: Select
      target architecture</term>

     <listitem>
      <para>Selects the target architecture.  The default architecture
       is <quote>x86</quote>, which supports both the IA-32 and
       derivatives and AMD64 instruction sets.  To print a list of
       available architectures to standard output, use
       <quote>help</quote> as <replaceable>arch</replaceable>.  See

       <citerefentry>
        <refentrytitle>yasm_arch</refentrytitle>
        <manvolnum>7</manvolnum>
       </citerefentry>

       for a list of supported architectures.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-f <replaceable>format</replaceable></option> or
      <option>--oformat=<replaceable>format</replaceable></option>:
      Select object format</term>

     <listitem>
      <para>Selects the output object format.  The default object
       format is <quote>bin</quote>, which is a flat format binary
       with no relocation.  To print a list of available object
       formats to standard output, use <quote>help</quote> as
       <replaceable>format</replaceable>.  See

       <citerefentry>
        <refentrytitle>yasm_objfmts</refentrytitle>
        <manvolnum>7</manvolnum>
       </citerefentry>

       for a list of supported object formats.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-g <replaceable>debug</replaceable></option> or
      <option>--dformat=<replaceable>debug</replaceable></option>:
      Select debugging format</term>

     <listitem>
      <para>Selects the debugging format for debug information.
       Debugging information can be used by a debugger to associate
       executable code back to the source file or get data structure
       and type information.  Available debug formats vary between
       different object formats; <command>yasm</command> will error
       when an invalid combination is selected.  The default object
       format is selected by the object format.  To print a list of
       available debugging formats to standard output, use
       <quote>help</quote> as <replaceable>debug</replaceable>.  See

       <citerefentry>
        <refentrytitle>yasm_dbgfmts</refentrytitle>
        <manvolnum>7</manvolnum>
       </citerefentry>

       for a list of supported debugging formats.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-h</option> or <option>--help</option>: Print a
      summary of options</term>

     <listitem>
      <para>Prints a summary of invocation options.  All other options
       are ignored, and no output file is generated.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-L <replaceable>list</replaceable></option> or
      <option>--lformat=<replaceable>list</replaceable></option>:
      Select list file format</term>

     <listitem>
      <para>Selects the format/style of the output list file.  List
       files typically intermix the original source with the machine
       code generated by the assembler.  The default list format is
       <quote>nasm</quote>, which mimics the NASM list file format.
       To print a list of available list file formats to standard
       output, use <quote>help</quote> as
       <replaceable>list</replaceable>.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-l <replaceable>listfile</replaceable></option> or
      <option>--list=<replaceable>listfile</replaceable></option>:
      Specify list filename</term>

     <listitem>
      <para>Specifies the name of the output list file.  If this
       option is not used, no list file is generated.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-m <replaceable>machine</replaceable></option> or
      <option>--machine=<replaceable>machine</replaceable></option>:
      Select target machine architecture</term>

     <listitem>
      <para>Selects the target machine architecture.  Essentially a
       subtype of the selected architecture, the machine type selects
       between major subsets of an architecture.  For example, for the
       <quote>x86</quote> architecture, the two available machines are
       <quote>x86</quote>, which is used for the IA-32 and derivative
       32-bit instruction set, and <quote>amd64</quote>, which is used
       for the 64-bit instruction set.  This differentiation is
       required to generate the proper object file for relocatable
       object formats such as COFF and ELF.  To print a list of
       available machines for a given architecture to standard output,
       use <quote>help</quote> as <replaceable>machine</replaceable>
       and the given architecture using <option>-a
        <replaceable>arch</replaceable></option>.  See

       <citerefentry>
        <refentrytitle>yasm_arch</refentrytitle>
        <manvolnum>7</manvolnum>
       </citerefentry>

       for more details.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-o <replaceable>filename</replaceable></option> or
      <option>--objfile=<replaceable>filename</replaceable></option>:
      Specify object filename</term>

     <listitem>
      <para>Specifies the name of the output file, overriding any
       default name generated by Yasm.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-p <replaceable>parser</replaceable></option> or
      <option>--parser=<replaceable>parser</replaceable></option>:
      Select parser</term>

     <listitem>
      <para>Selects the parser (the assembler syntax).  The default
       parser is <quote>nasm</quote>, which emulates the syntax of
       NASM, the Netwide Assembler.  Another available parser is
       <quote>gas</quote>, which emulates the syntax of GNU AS.  To
       print a list of available parsers to standard output, use
       <quote>help</quote> as <replaceable>parser</replaceable>.  See

       <citerefentry>
        <refentrytitle>yasm_parsers</refentrytitle>
        <manvolnum>7</manvolnum>
       </citerefentry>

       for a list of supported parsers.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-r <replaceable>preproc</replaceable></option> or
      <option>--preproc=<replaceable>preproc</replaceable></option>:
      Select preprocessor</term>

     <listitem>
      <para>Selects the preprocessor to use on the input file before
       passing it to the parser.  Preprocessors often provide macro
       functionality that is not included in the main parser.  The
       default preprocessor is <quote>nasm</quote>, which is an
       imported version of the actual NASM preprocessor.  A
       <quote>raw</quote> preprocessor is also available, which simply
       skips the preprocessing step, passing the input file directly
       to the parser.  To print a list of available preprocessors to
       standard output, use <quote>help</quote> as
       <replaceable>preproc</replaceable>.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--version</option>: Get the Yasm version</term>

     <listitem>
      <para>This option causes Yasm to prints the version number of
       Yasm as well as a license summary to standard output.  All
       other options are ignored, and no output file is
       generated.</para>
      </listitem>
     </varlistentry>
   </variablelist>
  </refsect2>

  <refsect2>
   <title>Warning Options</title>

   <para><option>-W</option> options have two contrary forms:
    <option>-W<replaceable>name</replaceable></option> and
    <option>-Wno-<replaceable>name</replaceable></option>.  Only the
    non-default forms are shown here.</para>

   <para>The warning options are handled in the order given on the
    command line, so if <option>-w</option> is followed by
    <option>-Worphan-labels</option>, all warnings are turned off
    <emphasis>except</emphasis> for orphan-labels.</para>

   <variablelist>
    <varlistentry>
     <term><option>-w</option>: Inhibit all warning messages</term>

     <listitem>
      <para>This option causes Yasm to inhibit all warning messages.
       As discussed above, this option may be followed by other
       options to re-enable specified warnings.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-Werror</option>: Treat warnings as errors</term>

     <listitem>
      <para>This option causes Yasm to treat all warnings as errors.
       Normally warnings do not prevent an object file from being
       generated and do not result in a failure exit status from
       <command>yasm</command>, whereas errors do.  This option makes
       warnings equivalent to errors in terms of this behavior.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-Wno-unrecognized-char</option>: Do not warn on
      unrecognized input characters</term>

     <listitem>
      <para>Causes Yasm to not warn on unrecognized characters found
       in the input.  Normally Yasm will generate a warning for any
       non-ASCII character found in the input file.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-Worphan-labels</option>: Warn on labels lacking a
      trailing option</term>

     <listitem>
      <para>When using the NASM-compatible parser, causes Yasm to warn
       about labels found alone on a line without a trailing colon.
       While these are legal labels in NASM syntax, they may be
       unintentional, due to typos or macro definition
       ordering.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-X <replaceable>style</replaceable></option>:
      Change error/warning reporting style</term>

     <listitem>
      <para>Selects a specific output style for error and warning
       messages.  The default is <quote>gnu</quote> style, which
       mimics the output of <command>gcc</command>.  The
       <quote>vc</quote> style is also available, which mimics the
       output of Microsoft's Visual C++ compiler.</para>

      <para>This option is available so that Yasm integrates more
       naturally into IDE environments such as <application
        class="software">Visual Studio</application> or <application
        class="software">Emacs</application>, allowing the IDE to
       correctly recognize the error/warning message as such and link
       back to the offending line of source code.</para>
     </listitem>
    </varlistentry>
   </variablelist>
  </refsect2>

  <refsect2>
   <title>Preprocessor Options</title>

   <para>While these preprocessor options theoretically will affect
    any preprocessor, the only preprocessor currently in Yasm is the
    <quote>nasm</quote> preprocessor.</para>

   <variablelist>
    <varlistentry>
     <term><option>-D
       <replaceable>macro[=value]</replaceable></option>: Pre-define a
      macro</term>

     <listitem>
      <para>Pre-defines a single-line macro.  The value is optional
       (if no value is given, the macro is still defined, but to an
       empty value).</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-e</option> or <option>--preproc-only</option>:
      Only preprocess</term>

     <listitem>
      <para>Stops assembly after the preprocessing stage; preprocessed
       output is sent to the specified output name or, if no output
       name is specified, the standard output.  No object file is
       produced.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-I <replaceable>path</replaceable></option>: Add
      include file path</term>

     <listitem>
      <para>Adds directory <replaceable>path</replaceable> to the
       search path for include files.  The search path defaults to
       only including the directory in which the source file
       resides.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-P <replaceable>filename</replaceable></option>:
      Pre-include a file</term>

     <listitem>
      <para>Pre-includes file <replaceable>filename</replaceable>,
       making it look as though <replaceable>filename</replaceable>
       was prepended to the input.  Can be useful for prepending
       multi-line macros that the <option>-D</option> can't
       support.</para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-U <replaceable>macro</replaceable></option>:
      Undefine a macro</term>

     <listitem>
      <para>Undefines a single-line macro (may be either a built-in
       macro or one defined earlier in the command line with
       <option>-D</option>.</para>

     </listitem>
    </varlistentry>
   </variablelist>
  </refsect2>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>To assemble NASM syntax, 32-bit x86 source
   <filename>source.asm</filename> into ELF file
   <filename>source.o</filename>, warning on orphan labels:

   <screen>yasm -f elf32 -Worphan-labels source.asm</screen></para>

  <para>To assemble NASM syntax AMD64 source
   <filename>x.asm</filename> into Win64 file
   <filename>object.obj</filename>:

   <screen>yasm -f win64 -o object.obj x.asm</screen></para>

  <para>To assemble already preprocessed NASM syntax x86 source
   <filename>y.asm</filename> into flat binary file
   <filename>y.com</filename>:

  <screen>yasm -f bin -r raw -o y.com y.asm</screen></para>
 </refsect1>

 <refsect1>
  <title>Diagnostics</title>

  <para>The <command>yasm</command> command exits 0 on success, and
   nonzero if an error occurs.</para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>Yasm's NASM parser and preprocessor, while they strive to be
   as compatible as possible with NASM, have a few incompatibilities
   due to YASM's different internal structure.</para>

  <para>Yasm's GAS parser and preprocessor are missing a number of
   features present in GNU AS.</para>
 </refsect1>

 <refsect1>
  <title>Restrictions</title>

  <para>As object files are often architecture and machine dependent,
   not all combinations of object formats, architectures, and machines
   are legal; trying to use an invalid combination will result in an
   error.</para>

  <para>There is no support for symbol maps.</para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <para><citerefentry>
    <refentrytitle>yasm_arch</refentrytitle>
    <manvolnum>7</manvolnum>
   </citerefentry>,
   <citerefentry>
    <refentrytitle>yasm_dbgfmts</refentrytitle>
    <manvolnum>7</manvolnum>
   </citerefentry>,
   <citerefentry>
    <refentrytitle>yasm_objfmts</refentrytitle>
    <manvolnum>7</manvolnum>
   </citerefentry>,
   <citerefentry>
    <refentrytitle>yasm_parsers</refentrytitle>
    <manvolnum>7</manvolnum>
   </citerefentry></para>

  <para>Related tools:
   <citerefentry>
    <refentrytitle>as</refentrytitle>
    <manvolnum>1</manvolnum>
   </citerefentry>,
   <citerefentry>
    <refentrytitle>ld</refentrytitle>
    <manvolnum>1</manvolnum>
   </citerefentry>,
   <citerefentry>
    <refentrytitle>nasm</refentrytitle>
    <manvolnum>1</manvolnum>
   </citerefentry></para>
 </refsect1>

 <refsect1>
  <title>Bugs</title>

  <para>When using the <quote>x86</quote> architecture, it is overly
   easy to generate AMD64 code (using the <userinput>BITS
    64</userinput> directive) and generate a 32-bit object file (by
   failing to specify <option>-m amd64</option> or selecting a 64-bit
   object format such as ELF64 on the command line).</para>
 </refsect1>
</refentry>
